Using 'boastful' often implies the speaker feels annoyance or disapproval towards someone's behavior. She found his boastful comments about the new car quite off-putting.
Pro Tip 2/3
Cultural Sensitivity
In some cultures, being boastful can be especially frowned upon and seen as lacking humility. Despite his success, he avoided any boastful remarks to respect his culture's values.
Pro Tip 3/3
Not Always Literal
Sometimes 'boastful' describes not just spoken words, but also actions that seem to show off. Her boastful display of awards made visitors feel uncomfortable.